SPINAL FIXING DEVICE DESCRIPTION OF THE INVENTION This invention relates to a device for fixing vertebrae adjacent to each other using a bar and unique hollow threads. Fixation (or fusion) of spinal columns with bone material or bars and plates is a surgical method practiced long ago common to treat a variety of conditions. Many of the existing procedures comprise components that protrude from the outside that can make contact and damage a part of the body, such as the aorta, the vena cava, the sympathetic nerves, the intestine and the urethra. Also, many constructions comprise components that can become loose and cause undesirable problems. A device of Dunn was in the market until being extracted by the Food and Drug Administration of the United States due to the problems with the delayed rupture of the aorta secondary to the device because it is too bulky in such a way that it makes contact with the aorta, erosion to its surface and leads to fatal hemorrhage in many cases. U.S. Patent 5,152,303 issued to Alien on October 6, 1992, refers to an anterolateral spinal fixation system that includes a cannulated thread threaded into a vertebra and a bar attached to the thread. The process involves threading the cannulated thread into a pilot hole punched into the body portion of the vertebra and attaching a bar at its lower and upper ends to the body of the vertebra by cannulated threads. (Column 3, lines 62-64, Column 4, lines 5-8). U.S. Patent 4,059,115 issued to Jumashev et al., November 22, 1977, relates to a surgical instrument for operation of anterior fenestrated spondylodesis in vertebral osteochondrosis. The instrument includes a hollow cylindrical cutter with a cutter edge and a handle. By rotating the handle accompanied by light pressure the cutter is made to work on the bodies of the adjacent vertebrae (extract, Column 6, lines 56-58). U.S. Patent 5,015,247 issued to Michelson on May 14, 1991 relates to a method for performing internal stabilization of a spinal column. The method comprises seating a drill sleeve in both vertebrae and piercing the vertebra with the drill installed through the drill sleeve. Bagby 4,501,269 is mentioned. (Column 6, lines 27-30, Column 7, line 68, Column 5, lines 22-25, 39). Current devices have substantial deficiencies when they encounter osteoporotic bone. The soft decalcified bone in such patients has a poor extraction strength for the threads. Bone threads are known to have very little holding power in osteoporotic bone and are easily released, severely limiting the fixation power and fixability of current devices. Some devices have designs that include hollow threads or threads with holes drilled transversely, presumably to improve the holding power and allow the bone to grow through them. These devices are all relatively small threads that are not capable of a large surface area fixation. The technique described in this section is not intended as an admission that any patent, publication or other information referenced herein is the "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be considered to mean that an investigation has been conducted or that there is no other relevant information as defined in 37 C.F.R. § 1.56 (a). The invention provides a method and device for fixing two or more vertebrae. The process is elegantly simple and solves many of the concomitant problems with previous devices.
Each vertebra that is going to be joined is prepared by using a partial ring cut, such as by a hole saw, preferably leaving the center hole of the bone in place. A hollow thread is threaded in the annular ring recess thus formed. A canal is cut in the vertebral bone between each of the threads to accommodate a bar that is placed over each thread. A closing cap on each thread secures the bar to the threads and thereby fixes the spine as desired. The method and device provide many advantages. The hollow threads are exceptionally strong, which have a larger clamping surface area than conventional solid threads. The bar is kept in the thread between two widely separated slots. The bar is also held firmly by a third point by a depression on the closure cap. The bar is secured to the threads by at least three fixing points over a much greater distance than traditional systems. This provides a link that is significantly greater in terms of mechanical stability over the prior art. The holes in the side walls of the hollow threads allow the bone to grow inside to further strengthen the connection. Because the hole in the bone is not removed, the wall of the threads is very thin, the bone can grow through the thread quickly, safely fusing the threads to the vertebrae and providing a better anchorage to the bone of the bones. vertebrae Additionally, as the bone grows through the holes in the thread, the bone becomes stronger over time. Prior art devices use threads that can slowly be less secure with age and the inevitable micromoción that occurs between the threading and the vertebral bone. By varying the geometric cross-sectional structure and the diameter of the bar, various degrees of stiffness can be imparted. Also, by varying the geometric cross section structure of the bar, the stiffness can be selectively imparted in the appropriate plane of movement. For example, if the increased flexion-extension stability is desired, the bar can be oriented in the flexion-extension plane and lengthened in such a way as to provide greater rigidity in flexion-extension than in the lateral bend. This aspect will allow the surgeon to define the level of rigidity necessary to face the pathology. The bars within the cutting channels avoid the bracket effect of the prior art devices where loading is performed away from the center of the spine.
Thus, the bar acts more like a bar intramedularly in the vertebrae. This is very preferable because a bar closer to the center of the axis of rotation does not have the bracket effect of prior art systems. This also has protrusions that can taper against vital body components. The process is very simple, requiring only the drilling of a single cut of individual hole saw in each vertebra, the formation of channels between them and the installation of the hollow threads, the placement of the bar and the assurance with closure caps . BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the invention is described below with specific reference to the drawings in which: FIGURE 1 is a perspective view of the device of the securing vertebrae of the invention together; FIGURE 2 is an exploded view of the bar, the thread, the lid and the prepared vertebrae; FIGURE 3 is a cross-sectional view taken along line 3-3 of Figure 1. FIGURE 4 is a cross-sectional view taken along line 4-4 of Figure 3; FIGURE 5a is a cross-sectional view taken along line 5-5 of Figure 4 showing the bar in cross section;FIGURE 5b is a cross-sectional view taken along line 5-5 of Figure 4 showing an alternate bar in cross section; FIGURE 5c is a cross-sectional view taken along line 5-5 of Figure 4 showing an alternate bar in cross section; FIGURE 5d is a cross-sectional view taken along line 5-5 of Figure 4 showing an alternate bar in cross section; FIGURE 5e is a cross-sectional view taken along line 5-5 of Figure 4 showing an alternate bar in cross section; FIGURE 6 is a cross-sectional view similar to Figure 3 with an overcap design; FIGURE 7 is an end view of a partially cut corpectomy block; FIGURE 8 is a tool for threading into the device in the annular ring recess in the body of the vertebra; FIGURE 9 is a perspective view of the corpectomy block of Figure 7; FIGURE 10 is a perspective view of a lockable wedge between the adjacent vertebrae; FIGURE 11 is a cross-sectional view of the wedge of FIGURE 10 along line 11-11;FIGURE 12 is a cross-sectional view of the wedge of FIGURE 10 - along line 12-12; FIGURE 13 is an alternative wedge in which an upper part is not planar; FIGURE 14 shows a section of a spine that needs realignment; FIGURE 15 shows the spine of FIGURE 14 with a corrective wedge in place; FIGURE 16 shows a spine that needs alignment, such as in the case of scoliosis; and FIGURE 17 shows the spine of FIGURE 16 in cross section, realigned with a corrective wedge. With specific reference to Figures 1 and 2 it will be noted that an anterior spinal fixation system 10 can join adjacent vertebrae together. The system includes an elongated bar 12 and at least two hollow cylindrical threads 14. Each thread 14 includes the external bone coupler fillets 16, the internal cap couplers 28, an upper edge 18 and a lower edge 20.
The internal fillets 28 only need to be as deep as the closing lid. A smooth inner wall is preferred to avoid placing the torque on the center of the remaining bone during thread insertion. As shown in Figure 2, the upper edge 18 is broken by two opposing bar fixing slots 22 which are dimensioned such that the bar 12 can pass in the slots 22, 24 as shown. Preferably, the threads 14 include a plurality of openings 36 of internal bone growth through the side walls which allow the bone to grow between them. The bar 12 is fastened to the threads by means of a closing cover 26. As shown, the closure cap 26 may be disk-shaped having the threads 30 around the circular periphery. The upper part 32 of the lid 26 can have a pair of spaced holes 34 to which a tool (not shown) can be connected to insert such a cover 26 into a hollow threaded thread 14. The cap 26 may be threaded in such a thread 14 such that no part of such a cap projects more than the thread 14. The cap may be porous and may have holes to allow the bone to grow inward and increase the blood supply to the bone. inside. Alternatively, as shown in FIGURE 6, the lid can be designed as an overcap 72 which engages the threads 74 on the external surface of the bone thread 14. As shown, the overcap 72 includes a cap projection 42 tapering against the bar 12. In the case of an overcap, some bone can be removed to accommodate the overcap as shown.
The rod 12 is preferably made of a biocompatible malleable metal such as titanium. A titanium bar has the advantage of having a modulus of elasticity similar to that of natural bone. In any case, the bar is bent by the surgeon to achieve the correct configuration desired for the patient. As shown in the Figures, the bar 12 may have a plurality of separate depressions 40 that may be round or elongated. The depressions 40 are face to face with a coupling projection 42. In the case of a round depression 40, the projection coupling 42 serves to prevent the sliding of the bar with respect to the thread 14. An elongated depression 40 allows a limited sliding which is sometimes desirable. Figures 5a-e show that the cross section of the bar 12 can be almost any shape other than round. Although a round cross-section bar would work, any non-round bar provides better torsion control. The size of the bar can be selected depending on the size of the individual patient. As previously stated, the cross-sectional shape of the bar can be altered to provide stability in the proper axis of motion for a particular patient. The installation of the device is direct. The surgeon exposes the vertebra 46 anteriorly and perforates a cylindrical opening 50 in the vertebral bone as shown in Figure 2-. Preferably, a hole saw is used to form the opening 50, since a hole saw will leave the center 52 in place. For ease of illustration, Figure 2 does not show a bone center 52, although the bone center 52 is shown in Figures 3 and 4. If a bone center 52 does not stay in place, the opening can be squeezed with the bone or bone substitute. It is to be noted that the bone opening 50 can be threaded if the perforator used is self-pruning or can be punctured by an additional tool used after drilling. Preferably, the implant threads 14 are slightly larger in external diameter than the outer diameter of the hole saw cut, thus providing a secure high friction bond to the body of the vertebra. This also provides a thread with an internal diameter slightly larger than the outer diameter of the center of the bone, thus reducing the possibility of torque from the center during the placement of the thread. Applying torque to the center in the insertion process can destroy the blood supply to the center. its rear surface. This would be undesirable since it can lead to a delayed incorporation of the bone closure capacity through the holes in the thread.
It is also possible to use a bone thread 14 of the device to cut its own thread 50. In such a case, the thread 14 is then left in place after being fully inserted. Each of the vertebrae adjacent to another bone opening 50 is then cut by a chisel or guiding tool to form a channel 54 of a depth to hold at least half the diameter of the bar 12. Although the vertebrae can be connected Without the channel using the device and the methods of this invention, many of the advantages are lost if at least most of the bar is not in a channel 54. The bone threads 14 are then threaded into the bone openings 50 with the fillets 28, 16 on the inside and outside of the bone threads 14 that couple the vertebral bone. The threads are positioned in such a way that the bar fixing slots 22, 24 align with the bone channels 54. A tool 58 as shown in Figure 8 can be used to thread the bone threads 14 into the bone openings 50. As shown, the tool 58 includes an arrow 60 with a handle 62 on one end and a thread coupling head 64 on the other end. The thread coupling head 64 includes a pair of tabs 6668, which engage with the slots 22, 24. The head 64 fits closely into the interior of the thread 14. No part of the tool 58 projects beyond the outer circumference of the bone threads 14. A bar 12 of the required length is then bent into the required shape and inserted into each thread through the bar fixing slots 22, 24 and into the bone channels 54 formed. The bar 12 can be removed to adjust the curvature of the spine that will be defined by the installed system as needed. Once the degree of correction has been achieved, the bar is held captively in place by securing a closure cap 26 on each thread 14 thereby trapping the bar 12 in place. The threads 14 of the bone are preferably placed in the vertebral bone at a considerable depth, leaving a safety zone of approximately 3 mm. Depending on the size of the vertebrae, the thread diameters can vary from 1.5 to 3.5 cm. Preferably, the diameter of the threads 14 is sufficient to cut the hardest, outer bone of the vertebrae. The threads 14 can have a relatively thin cylindrical wall and still provide great strength and holding power. The installed system of the invention provides a spinal correction with many important advantages. Because the cylindrical threads have a much larger surface area than a conventional solid thread, the holding power is much greater. The installed system is contained entirely within the confines of the vertebral bone. Nothing projects outward that may be in contact with the structures of the adjacent body. The bar 12 is much closer to the center of the vertebra which means that undesirable bracket effects such as prior art devices are greatly reduced. The system of the invention can be used to stabilize many or only two vertebrae. It can be used to provide corrections due to tumors, fractures, degenerative conditions, deformity or infection. The unrounded bar used in most cases provides longitudinal rotary control. The normal healing process of the body will cause bone growth around the threads, rods and lids to close the system even more securely to the vertebra. The threads 14 may include perforations through the length of the cylinder to allow internal growth in the bone that can increase the holding power. Figures 1, 7 and 9 show that the invention can be used between two or more adjacent vertebrae and can be used in conjunction with a corpectomy block 80 that functions as a spacer for a removed vertebral body. A block 80 of corpectomy is used when a large portion of the vertebral body has been removed, such as when removing a tumor, fractured bone or in cases of massive bone loss. Most of the vertebra is removed previously forming a space between the remaining vertebrae. The solution of the prior art is to provide a number of filling plates with bars or a large ceramic block anchored with conventional plates and threads. U.S. Patent 5,192,327 shows a suitable corpectomy block, which simply needs to be designed with a slot through which the bar 12 can pass. In Figure 7 and 9 a block 80 of corpectomy is shown in which the block is substantially hollow and is formed from material compatible with the body such as titanium or ceramic. The block may be porous or at least rough at the ends to allow growth in the bone. A filler port 82 can be constructed in block 80 to allow the addition of bone graft. The block 80 includes a longitudinal slot 84 through which the bar 12 can pass. In use, a block 80 fits the appropriate size between the remaining vertebrae after resection and fills up cor. Bone graft. The bar 12 is positioned through the slot 84 and is held in each bone thread 14 by the end caps 26 or 72. This firmly holds the corpectomy block 80 in place to allow the fusion of bone to the adjacent vertebrae as shown in Figure 1. The block must allow vascular growth by having at least the plates 8688 extreme porous. Block 80 may be porous titanium or ceramic with rough end plates. Figure 1 shows that the invention will work even if one or more vertebrae are resected and repositioned with a corpectomy block. In all forms of the invention, the hollow threads 14 provide greater holding power and allow an intramedullary rod that eliminates the cantilever structures found in pedicle screw systems of the prior art such as in U.S. Patent 5,324,290 issued June 28, 1994. The present invention directs the forces from near the center of the vertebrae and therefore the axis of forces in motion. In some cases, the spinal column needs realignment, facing the back, side by side, or both. Figures 10 to 17 show means for correcting alignment while using the spinal fixation device 10 of the invention. Figures 10 to 13 show the wedges that can be inserted between the vertebrae in the place of a removed disc. The wedge 90 of Figures 10-12 may be a solid ceramic block, it may be a wedge of titanium or any other material implantable in the body that can replace a disc. The anterior side 92 of the wedge 90 is higher than the trailing edge 94. A groove 96 is formed to allow the rod 12 to pass therethrough. The wedge 100 of FIGURE 12 includes a body formed in a similar manner, including a slot 96, but not a directional wedge. Either, a surface 102 of the wedge 100 is rounded or otherwise non-planar. In this form, the wedge 10 with a surface 102 against a vertebra can allow the rotational or angular correction of the deformity. The wedges 100 can be inserted to displace the disc, forming a clam shell appearance in which both adjacent vertebrae rest against a rounded surface 102. FIGURES 14 through 17 show how a wedge of the invention can be used to correct a defect of spinal alignment. In FIGURES 14 and 15, a spinal column consisting of the vertebra 104, 106 is out of alignment with respect to the spine stippled forward. In FIGURE 15 each vertebra includes a thread 14, a bar 12 and a wedge 90 which, by virtue of its greater anterior height, corrects the alignment. This method can be used instead of bending bar 12 to obtain similar results, or in conjunction with a bent bar.
FIGS. 16 and 17 show a typical scoliosis of the spine in which a corrective wedge 90 is slid from the side in such a way that the thickest portion of the wedge 90 is on one side, thereby correcting the curvature . In all cases, the wedge is inserted into the position, the vertebrae are allowed to be in contact with the wedge and the closure lids 26 and to be threaded in engagement with the bar 12 and to maintain the entire structure as desired. The invention can be used anteriorly, anterolaterally and laterally depending on the needs of the patient. The drawings show the previous use of the bone threads as a possible position. While this invention can be modalized in many different ways, specific preferred embodiments of the invention are shown in the drawings and are described in detail herein. The present description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. This completes the description of the preferred and alternative embodiments of the invention. Those skilled in the art will recognize others equivalent to the specific embodiment described herein whose equivalents are intended to be encompassed by the claims appended thereto.